That was it.
Indeed. Same at my end.
I was under impression that some people like yourself actually got it working and I just need to tweak things out: What is the best way to play blu-ray / BDMV movies? - #13 by balko
Some points to note:
- Top Gun’s dogfight scene with the same frame size as yours above plays smoothly even with 4k, especially at 0:15 and 1:06
- There’s definitely something with how Qubes/Xen renders video. I see significant difference between non-Qubes and Qubes versions of these tests: